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A scientific justification and technical description is developed for the construction of a Low Frequency Space Array (LFSA) to carry out full sky mapping and individual source imaging at frequencies between 1.5 and 26.3 MHz; a frequency range over which the Earth's ionosphere transmits poorly or not at all. Such an instrument, with high resolution and high sensitivity, will open a new window in the electromagnetic spectrum to astronomical investigations. It will also bring astronomy to the fundamental limit below which observations from within the Milky Way become impossible due to absorption by the diffuse ionized hydrogen component of the interstellar medium. Many high quality scientific programs can already be specified for such an instrument and, due to the fact that it will be operating in essentially unexplored ranges of freqency, sensitivity and resolution, the likelihood of discovering entirely unexpected objects and processes is large. Also, even though the technology for constructing the elements of the LSFA already exists, its operation as an entirely space based synthesis interferometer will represent a significant advance in space capability. Keywords include: Interferometry, Array, Imaging, Astronomy, Space, and Low frequency.

A large millimeter wavelength interferometer array is proposed for construction on the planned Space Station (The Space Station Microwave facility-SSMF). It will have manifold applications in both basic and applied research and will be the premier instrument in the world at high radio frequencies. All weather target detection and identification, earth resource mapping, middle atmospheric studies, ionospheric research, atmospheric infrared background investigations, interplanetary communications, and high frequency radio astronomy are only a few of the areas which will be significantly advanced by the availability of such an instrument. Particularly in astronomy, the ability to do observations above the disturbing and absorbing effects of the Earth's atmosphere will allow new opportunities for exploration of all objects from the Sun, through the Solar System bodies, to the interstellar medium of the Milky Way and other galaxies, out to the most distant quasars with resolution and sensitivity equalling or exceeding all existing or planned millimeter wavelength telescopes., Original contains color plates: All DTIC and NTIS reproductions will be in black and white.

With the proven techniques of radio astronomy and the rapidly advancing technology of space science, it is clear that the expansion of radio astronomy arrays beyond the limits of the Earth's surface is called for. Therefore, a preliminary discussion of the design and capability fo a purely space based array is presented. The science which can be done with such a high resolution, high sensitivity radio telescope array is discussed and a number of the parameters of a system are developed. A coherent interferometer array is possible with reasonable extensions of parameters of a system are developed. A coherent interferometer array is possible with reasonable extensions of parameters of a system are developed. A coherent interferometer array is possible with reasonable extensions of present technology and such a telescope will lead to major advances ind the areas of astrometry, the study of radio stars and radio supernovae, the investigation of astronomical masers, and the determination of the properties of the Milky Way nucleus and the active regions of normal galaxies, radio galaxies, and quasars. It is clear that an array of high orbit radio antennas linked to the low orbit Space Station represents the next logical step in the progression to continually higher resolution and sensitivity for radio astronomy. Keywords include: Interferomety; Array; Imaging; Astronomy; and Space.

Very long baseline interferometer observations at 4997 MHz (lambda = 6 cm) on European and intercontinental baselines with lengths up to 1.35 108lambda have been used to probe the milliarc s structure of the BL Lacertae objects AO 0235+164, 0735+178, BL Lac, 1749+701, Mk 421, and 3C 66A. Two sets of observations are reported, made in November 1978 and March 1979. AO 0235+164 and 0735+178 both showed structures consisting of a very bright, unresolved core and a jet-like component extending ˜5".4 10-3 along position angle ˜20° and ˜4".2 10-3 along position angle ˜45°, respectively. AO 0235+164 contained more than 98% of the total flux density within a diameter of ≲ 36" 10-3. BL Lac, 1749+701 and Mk 421 all showed evidence for a complex structure of several components, including an unresolved core. 3 C 66A was elongated along position angle ˜ -45°., Uppgifter om finansiärer finns. / JO 150817

At the lowest radio frequencies (<30 MHz), the Earth's ionosphere transmits poorly or not at all. This relatively unexplored region of the electromagnetic spectrum is thus an area where high resolution, high sensitivity observations from space can open a new window for astronomical investigations. An array of free flying spacecraft which work as a coherent interferometer will be able to probe this frequency range. Operating from ≡1 to ≡30 MHz, such a telescope will extend astronomy from just above the ionospheric cutoff, where ground based observations can still be done, down to the fundamental physical limit where observations at still lower frequencies from within the Milky Way are impossible due to absorption by diffuse, ionized interstellar hydrogen. The scientific rewards of such a space mission are likely to be great.

The total intensity and linearly polarized emission from the Crab Nebula (Taurus A) were synthesized to a resolution of approximately 1 arc-minute at both 1420 and 2880 MHz. From these data were calculated the spectral index, rotation measure, intrinsic position angle, and depolarization ratio distributions. Then, combined with a source model, the physical conditions within the supernova remnant were established. The strength and orientation of both the homogeneous and random components of the magnetic field were determined and a measurement of the thermal electron plasma distribution obtained.

One-dimensional distributions of the total and linearly polarized radiation from 3C227, 3C270, 3C278 Cen A (central), 3C327, Her A, 3C353, and 3C403 have been obtained at frequencies of 1420 and 2880 MHz. Both right-ascension and declination scans are presented. Distributions of depolarization, rotation measure, and intrinsic polarization angle are calculated. Variations of spectral index within sources are noted. The magnetic field near the center of many radio galaxies is perpendicular to the major axis; in the outer components it is either approximately perpendicular or parallel. Correlations are found between rotation measure and depolarization rate in some cases. (Author)

During its occultation by the sun in October 1969, the position of the radio source 3C279 was interferometrically monitored to determine the deviation of its 9.602-GHz radiation in the solar gravitational field. Rapid instrumental calibration and negligible coronal diffraction enabled the measurement of a General Relativity deflection of 1.77 plus or minus 0.20 seconds at the limb of the sun. This is in close agreement with Einstein's prediction. (Author)

An earth-rotation aperture-synthesis technique was combined with the methods of interference polarimetry to study the total intensity and linear polarization properties of the two radio sources 3C10 and 3C58 with a resolution of approximately one minute of arc at both 1420 and 2880 MHz. These data were then used to calculate the distributions of spectral index, rotation measure, intrinsic position angle, and polarization for the sources. (Author)

The distributions along a circle of constant declination of the linearly polarized radiation at a frequency of 1418 MHz from 68 extragalactic radio sources were examined. The effective resolution was about 0.8. At places within many sources very high degrees of polarization (> 15 per cent), usually accompanied by a constant plane of polarization, were found. Both facts imply the existence of a highly ordered magnetic field. Often other regions within the same source also contained uniform fields, but oriented differently. Less frequently the field is well-ordered over an entire component or even over the entire source. These regions of uniformity can exceed galactic dimensions (about 100 kpc). (Author)

As part of a continuing study employing the Owens Valley Radio Observatory's twin-element interferometer to provide high angular resolution measurements of the various radio source properties the Fourier transforms of the distributions of the Stokes parameters Q, U, and V were measured at several antenna spacings along an east-west baseline. The present paper catalogs these measurements, while a subsequent paper will interpret them in terms of the structure of the polarized radiation along a circle of constant declination. (Author)

Distributions of the linearly polarized radiation at a frequency of 1418 MHz from the four supernova remnants 3C 10 (Tycho's supernova), Taurus A (Crab Nebula), 3C358 (Kepler's supernova), and Cassiopeia A have been determined by synthesizing a fan beam whose small dimension is along a circle of constant declination. In addition, extremely low upper limits have been placed on the net degree of circular polarization in the integrated radiation from Tau A, 3C358, and Cas A. For the latter two sources, no smaller circularly polarized regions were found within the source dimensions using a resolution of better than 1'. Upper limits to the magnetic field strengths, modified by geometrical factors have also been calculated. (Author)